IFNAR dimerization observed for different IFN subtypes and mutants. (a) Relative number of colocomotion trajectories detected in the absence of ligand, in the presence of wt IFNα2, and in several IFNα2 mutants with increased and decreased binding affinities toward IFNAR1and IFNβ (each 50 nM) and IFNα2-M148A (200 nM). The broken line separates different types of mutants. (b) Affinity–dimerization relationship and plot of the law of mass action for naive and primed cells (data points are mean values taken from d). Dimerization for IFNβ is included as well as for IFNα2-wt under JAK inhibition. (c) Receptor dimerization in U5A^{IFNAR1/IFNAR2} cells in the absence and presence of 50 nM IFNα2, and after priming and ectopic expression of (EGFP)-USP18. (d) Comparison of colocomotion events for 50 nM IFNα2-wt and mutants observed with naive (red) and primed cells (blue). Box plots indicate the data distribution of the second and third quartile (box), median (line), mean (closed squares), and whiskers (1.5× interquartile range).